The present invention generally relates to information recording discs, and more particularly to an information recording disc having a guide track pre-formed thereon for determining a track position where an information signal is to be recorded and having an address signal pre-recorded on the guide track.
An information recording disc (hereinafter simply referred to as a disc) comprising a recording surface which is divided into a plurality of imaginary equiangular sectoral regions, where each track turn of the guide track is constituted by a row of pits formed in every other of the equiangular sectoral regions, each pit is only formed in one of two mutually adjacent track turns of the guide track in each of the equiangular sectoral regions so that the pits are formed in every other track turns of the guide track in a radial direction of the disc in each of the equiangular sectoral regions, and a track position where an information signal is to be recorded is located in a region between the two mutually adjacent track turns of the guide track was previously proposed in a U.S. patent application Ser. No. 873,407 filed June 12, 1986 in which the assignee is the same as the assignee of the present application. According to this disc, it is possible to obtain a tracking error signal from signals reproduced from the guide track by a main light beam. Hence, although a conventional disc having two continuous spiral guide tracks (grooves) located on both sides of an information signal recording track suffers a problem in that a trailing sub light beam is affected by pits of an information signal recorded by a main light beam at the time of the recording, it is possible to eliminate such a problem. In addition, by selecting a depth of the guide track to 1/4 the wavelength of the main light beam which is used for recording and reproducing the information signal, it is possible to prevent diffraction in a reflected light from the guide track. For this reason, the tracking error signal will not be affected by diffracted light even when the main light beam traverses the guide track. As a result, an astigmatic focusing method can be used as a method of detecting a focal error, and the construction of an optical system in a recording and reproducing apparatus can be simplified compared to that of a recording and reproducing apparatus which is designed exclusively for playing a conventional disc having a single continuous spiral guide track.
However, no address signal is pre-recorded on the above described disc. Hence, when the recording of the information signal is once discontinued at a predetermined position on the recording surface of the disc and the recording is to be resumed after a predetermined time so as to newly record an information signal from the predetermined position where the previous recording had been discontinued, it is extremely difficult to find the predetermined position. Furthermore, even when an address signal is recorded together with the information signal at the time of the recording, the track position cannot be detected with a high accuracy at the time of the reproduction by use of such an address signal compared to the case where the address signal is pre-recorded on the disc, because signal dropout or the like may occur at the time of the recording.
Hence, a disc having a control signal such as an address signal pre-recorded on a guide track which is pre-formed on the disc independently of an information recording track was previously proposed in a U.S. patent application entitled "INFORMATION RECORDING DISC AND INFORMATION SIGNAL RECORDING APPARATUS THEREFOR" filed Oct. 9, 1986 Ser. No. 917,188 in which the assignee is the same as the assignee of the present application. Since the address signal is pre-recorded on the guide track in such a frequency band or recording interval that each information in the information signal which is to be recorded is unaffected by the address signal, it is possible to constantly detect the track position and the like during the recording mode in which the information signal is recorded. For example, the address signal is pre-recorded between two successive pits in each track turn of the guide track, and the same address information is recorded at two positions in each track turn of the guide track.
When a main light beam for recording and reproducing the information signal accurately scans a region between two mutually adjacent track turns of the guide track and first and second sub light beams for tracking respectively scan the two mutually adjacent track turns of the guide track of this second disc, a sum of signals reproduced from the two mutually adjacent track turns of the guide track by the first and second sub light beams should in principle become zero because the pits are formed in every other track turns of the guide track in each equiangular sectoral region and the recording lengths of the pits can be assumed to be the same in the two mutually adjacent track turns of the guide track. However, the recording length of an address signal recording portion between the two successive pits in each track turn of the guide track is selected to be within the vertical blanking period so as not to coincide with the recording interval of the information signal (for example, a frequency converted carrier chrominance signal which has been frequency-converted into a low frequency band) having a frequency band identical to that of the address signal and to avoid the interval of the color burst signal. For this reason, the recording length of the address signal recording portion in which the address signal is recorded is always shorter than the recording length (one horizontal scanning period) of the pit. As a result, due to the existence of the address signal recording portion, the sum of the signals reproduced from the two mutually adjacent track turns of the guide track by the first and second sub light beams does not become zero. Since a tracking control operation is carried out based on the two signals reproduced from the two mutually adjacent track turns of the guide track, there is a problem in that the tracking control operation becomes unstable according to this disc.